The invention is concerned with a ventilation and aeration device for a fuel tank, in particular of a motor vehicle, having a ventilation line which leads to the exterior of the fuel tank and is connected to the inner area of the fuel tank via a ventilation opening of a ventilation link of larger through-flow cross section and an aeration opening of an aeration link of smaller through-flow cross section, the ventilation opening of the ventilation link leading into the inner area of the fuel tank at a filling level height which is lower than the aeration opening of the aeration link, and a roll-over valve being used to seal off the inner area of the fuel tank from the ventilation line.
In the case of ventilation and aeration devices of this type, the ventilation opening and ventilation link are used to conduct gas which has been displaced in the fuel tank by the fuel fed in during a refueling process to the outside. If, during the refueling process, the filling level reaches the level of the ventilation opening and the latter is covered in the process by the fuel, gas can no longer be conducted away through the ventilation opening. The fuel which flows in from the refueling and acts on the rest of the volume of gas in the fuel tank causes a pressure to be built up in the fuel tank, the pressure acting on the tank nozzle introduced into the filler neck of the fuel tank and actuating the automatic cutoff contained in this tank nozzle. Further filling of the fuel tank is therefore terminated.
The aeration opening, which is situated higher than the ventilation opening, has only a small cross section which acts as a throttle and through which gas cannot be conducted away sufficiently in order to prevent the described build-up of pressure during refueling.
The ventilation opening serves to conduct away a volume of gas, which becomes enlarged when there is a rise in temperature, to the outside, so that a rise in pressure in the fuel tank does not take place.
In order to prevent fuel from being able to run out of the fuel tank via the ventilation and aeration openings if the motor vehicle is in an accident and overturns, the roll-over valves seal off the ventilation and aeration openings in the corresponding position of the motor vehicle.
In the case of a ventilation and aeration device of the type mentioned at the beginning, it is known to design both the ventilation opening and the aeration opening in a manner such that they can be sealed off in each case by a roll-over valve. The construction of this ventilation and aeration device is very complex and expensive and requires a large structural space.
EP 186 372 A discloses a ventilation and aeration device for a fuel tank having a ventilation line which leads to the exterior of the fuel tank and is connected to the inner area of the fuel tank via a ventilation opening of a ventilation link of larger through-flow cross section and an aeration opening of an aeration link of smaller through-flow cross section. In this case, the ventilation opening of the ventilation link leads into the inner area of the fuel tank at a filling level height which is lower than the aeration opening of the aeration link.
U.S. Pat. No. 5,215,132 A discloses a ventilation and aeration device for a fuel tank, having a ventilation line which leads to the exterior of the fuel tank and is connected to the inner area of the fuel tank via a ventilation opening of a ventilation link of larger through-flow cross section and a further ventilation opening. The ventilation line can be sealed off from the inner area of the fuel tank by a first roll-over valve, to the outlet of which the ventilation line is connected. A second ventilation line leading to the exterior of the fuel tank can be sealed off by a second roll-over valve.
The object of the invention is therefore to provide a ventilation and aeration device of the type mentioned at the beginning which has a simple construction and requires only a small structural space.